Keep plain-string custom metrics

[max-ostapenko]

This pull request makes a minor change to the error handling in the get_custom_metrics function. Specifically, it no longer logs a warning when a custom metric value cannot be parsed as JSON and instead simply keeps the value as a plain string.

[Copilot]

Pull request overview

This PR modifies the error handling in the get_custom_metrics function to preserve plain-string custom metric values instead of discarding them when JSON parsing fails. Previously, when a ValueError occurred during JSON parsing, the metric was skipped entirely with a warning logged. Now, the code keeps the original string value as-is.

• Changed ValueError exception handling from logging a warning and skipping the metric to keeping the value as a plain string
• Added an inline comment explaining the new behavior

Comments suppressed due to low confidence (1)

HTTPArchive/httparchive.py:140

• Inconsistent error handling: The ValueError exception now keeps the value as a plain string (using pass), but the RecursionError exception still skips the metric entirely (using continue). Consider whether RecursionError should also keep the original string value for consistency, or if there's a specific reason to treat these errors differently.

                # Value is a plain string, not JSON-encoded. Keep it as-is.
                pass
            except RecursionError:
                logging.warning(
                    "RecursionError: Unable to parse custom metric %s as JSON for %s",
                    metric,
                    wptid,
                )
                continue

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